Mixer that performs reciprocating rotary motion for a confluent-flow nozzle of a turbine engine, and a method of controlling it

1. A mixer for a confluent-flow nozzle of a turbine engine, the mixer comprising:

an annular cap designed to be centered on a longitudinal axis of the confluent-flow nozzle, the annular cap having a stationary upstream portion and a downstream portion that is movable in rotation about the longitudinal axis relative to the stationary portion, a downstream end of the movable portion of the annular cap terminating in inner lobes alternating circumferentially with outer lobes; and

a reciprocating rotary motion imparting mechanism which imparts reciprocating rotary motion to the movable portion of the cap.

2. The mixer according to claim 1 , wherein the movable portion of the annular cap is connected to the stationary portion of the annular cap via a rack-and-pinion type connection.

3. The mixer according to claim 2 , wherein the stationary portion of the annular cap has a rotary electric motor coupled to a pinion meshing with a rack secured to the movable portion of the annular cap.

4. The mixer according to claim 1 , wherein an angular amplitude of the reciprocating rotary motion of the movable portion of the annular cap corresponds substantially to a width of one lobe.

5. The mixer according to claim 1 , wherein a frequency of the reciprocating rotary motion of the movable portion of the annular cap lies in the range 0.1 hertz (Hz) to 10 hertz (Hz).

6. The mixer according to claim 5 , wherein the frequency of the reciprocating rotary motion of the stationary portion of the annular cap is 1 hertz (Hz).

7. A confluent-flow nozzle for a turbine engine including a mixer according to claim 1 .

8. A turbine engine including a confluent-flow nozzle according to claim 7 .

9. The mixer according to claim 1 , wherein the inner lobes and the outer lobes are each formed by a pair of walls extending in a substantially radial direction, being spaced apart in a circumferential direction, and being connected by arches.

10. The mixer according to claim 9 , wherein the arches of the inner lobes are connected at radially inner ends of the walls.

11. The mixer according to claim 9 , wherein the arches of the outer lobes are connected at radially outer ends of the walls.

12. A method of controlling a mixer according to claim 1 , comprising:

causing the movable portion of the annular cap of the mixer to perform reciprocating rotary motion at least during a takeoff stage.

13. The method according to claim 12 , wherein the reciprocating rotary motion of the movable portion of the annular cap of the mixer is deactivated during a cruising stage.